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, 278 (1708), 1090-7

Correlates of Rediscovery and the Detectability of Extinction in Mammals

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Correlates of Rediscovery and the Detectability of Extinction in Mammals

Diana O Fisher et al. Proc Biol Sci.

Abstract

Extinction is difficult to detect, even in well-known taxa such as mammals. Species with long gaps in their sighting records, which might be considered possibly extinct, are often rediscovered. We used data on rediscovery rates of missing mammals to test whether extinction from different causes is equally detectable and to find which traits affect the probability of rediscovery. We find that species affected by habitat loss were much more likely to be misclassified as extinct or to remain missing than those affected by introduced predators and diseases, or overkill, unless they had very restricted distributions. We conclude that extinctions owing to habitat loss are most difficult to detect; hence, impacts of habitat loss on extinction have probably been overestimated, especially relative to introduced species. It is most likely that the highest rates of rediscovery will come from searching for species that have gone missing during the 20th century and have relatively large ranges threatened by habitat loss, rather than from additional effort focused on charismatic missing species.

Figures

Figure 1.
Figure 1.
Cox proportional hazards regression showing the mean difference in the probability of rediscovery between species affected by different threats, in all centuries. Habitat loss (including fragmentation and degradation), dotted line; introduced species (including invasive diseases and predators), dashed line; overkill (including harvesting, persecution and exploitation), solid line. The y-axis shows the probability of rediscovery for each category per year. Time zero is when all species in the category are missing (0 = zero rate of rediscovery, 1 = 100% rediscovered). Cox proportional hazards regression does not extrapolate beyond the data: the curve for species affected by habitat loss ends at 180 years because the earliest suspected extinction attributed to habitat loss was 180 years ago (the Bahian tree rat, Phyllomys unicolor). Several species affected by introduced species or overkill disappeared in the 16th century (n = 187).
Figure 2.
Figure 2.
Frequency distribution of the number of reported searches targeting particular missing species, in all centuries. Rediscovered species are white bars, missing species are black bars. Species with high numbers of searches (≥12, all unsuccessful) are Pemberton's deer mouse (Peromyscus pembertoni) and the Angel Island deer mouse (Peromyscus guardia) from Mexico; the baiji (Lipotes vexillifer) from China; wild horse (Equus ferus) from China, Mongolia, Belarus, Germany, Kazakhstan, Lithuania, Poland, the Russian Federation and Ukraine; kouprey (Bos sauveli) from Thailand, Laos and Cambodia; and the thylacine (Thylacinus cynocephalus) from Australia (for an explanation of sources for search effort, see electronic supplementary material, text S1; n = 178).
Figure 3.
Figure 3.
Cox proportional hazards regression showing mean probability of rediscovery for species affected by habitat loss in seven categories of range size. All species were last recorded in the 19th or 20th century. (a) Small geographical ranges (thick solid line, <1 km2; thick dotted line, 1–10 km2; thin solid line, 11–100 km2; thin dotted line, 101–1000 km2); (b) larger geographical ranges (thick solid line, 1001–10 000 km2; dotted line, 10 001–100 000 km2; thin solid line, 100 001–1 000 000 km2). Time zero is when all species in the category are missing (0 = zero rate of rediscovery, 1 = 100% rediscovered; n = 164).

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